1. Field of the Invention
The present invention relates to an optical disc player, and more particularly, to a tilt adjusting apparatus to adjust a tilt of an optical pickup so that a light beam emitted from the optical pickup is perpendicularly incident on a recording surface of a disc.
2. Description of the Related Art
Generally, an optical disc player records data or reproduces recorded data by irradiating a light beam on an optical recording medium such as a compact disc (CD) or a digital video disc (DVD). To perform the above job, the optical disc player includes a turntable on which a disc is laid, a spindle motor for rotating the turntable, and the optical pickup that performs recording and reproduction of data by irradiating the light beam on the recording surface of the disc.
In such an optical disc player, the light beam emitted from the optical pickup is required to be perpendicularly incident on the recording surface of the disc, to form a spot of the light beam of a correct focus. But due to manufacturing and assembly problems, it is difficult to keep the disc parallel to a main base provided with a guide shaft for guiding the transfer motion of the optical pickup or the spindle motor for supporting and rotating the disc. Since a distance between the disc and the optical pickup changes depending on the movement of the optical pickup, the incident direction of the light beam is not accurately perpendicular to the recording surface of the disc. As described above, if the incident direction of the light beam deviates, the correct spot of the light beam cannot be formed on the recording surface of the disc, and errors may be generated in recording or reproducing data. Thus, the light beam can be made perpendicularly incident on the recording surface of the disc by keeping the disc and the optical pickup parallel to each other, to form a correctly focused spot of the light beam. This is referred to as a tilt adjustment or a skew adjustment.
FIG. 1 shows a main base of an optical disc player with a conventional tilt adjusting apparatus.
As shown in FIG. 1, the optical disc player includes a spindle motor 20 for rotating a disc (not shown), and an optical pickup 30 that performs recording and reproduction of data by irradiating a light beam on a recording surface of the disc. A turntable 22 to accommodate the disc is positioned on an upper portion of the spindle motor 20. The optical pickup 30 includes various optical components such as a pickup base 34 and an objective lens 32 mounted on the pickup base 34. The spindle motor 20 and the optical pickup 30 are assembled onto a main base 10. The main base 10 is installed in a disc tray of the optical disc player or a main frame of a housing. The main base 10 is provided with an opening 12, in which to move the optical pickup 30.
The optical pickup 30 moves along a radial direction of the disc, and irradiates the light beam on the recording surface of the disc. To move the optical pickup 30, the main base 10 is provided with an optical pickup transfer unit 40. The optical pickup transfer unit 40 includes a lead screw 46 to linearly move the optical pickup 30 by its rotation, a driving motor 42, and a connection gear group 44 to transmit power from the driving motor 42 to the lead screw 46. Two guide shafts 51 and 52 are positioned at opposing sides of the optical pickup 30 to guide the reciprocating linear movement of the optical pickup 30.
The main base 10 is provided with a tilt adjusting apparatus for adjusting the tilt of the optical pickup 30. The tilt adjusting apparatus adjusts a distance between the recording surface of the disc and the optical pickup 30 by adjusting the inclinations of the two guide shafts 51 and 52 using two adjusting screws 61 and 62 and two leaf springs, respectively.
FIG. 2 is a cross-sectional view showing a structure incorporating the guide shaft with the tilt adjusting apparatus of FIG. 1, and FIG. 3 is a cross-sectional view to explain problems of the conventional tilt adjusting apparatus generated when the guide shafts 51 and 52 shown in
FIG. 2 are over-adjusted. Since the above incorporating structure is the same at both guide shafts 51 and 52, only the incorporating structure of one guide shaft 51 will be described.
Referring now to FIG. 2, an end of the guide shaft 51 closest to the spindle motor 20, a supporting end 51a, is positioned inside the circumference of the disc D, and is inserted into and supported by a supporting groove 14 in the main base 10. Since the supporting groove 14 prevents the supporting end 51a from moving up and down, the supporting end 51a functions as a hinge point when an adjusting end 51b of the guide shaft 51 moves up and down.
The adjusting end 51b of the guide shaft 51 is movably supported by the adjusting screw 61 and the leaf spring 71. The adjusting screw 61 is coupled with a bracket 16 installed at the main base 10, and the lower portion of the adjusting screw 61 contacts an upper surface of the adjusting end 51b of the guide shaft 51. The bracket 16 may be manufactured as part of the main base 10 using standard injection mold technology. In recent optical disk drives, however, the bracket 16 is made of a metallic plate having a thickness of 0.8–1.0 mm, which is incorporated into the main base 10.
A first end of the leaf spring 71 is fixed to a lower surface of the main base 10 by a locking screw 73. A second end of the leaf spring 71 contacts a lower surface of the adjusting end 51b of the guide shaft 51 and applies an elastic force upward. Since the adjusting end 51b of the guide shaft 51 moves up and down by tightening or loosing the adjusting screw 61, the inclination of the guide shaft 51, and thereby the tilt of the optical pickup 30 guided by the guide shaft 51, is adjusted.
In the conventional tilt adjusting apparatus, as shown in FIG. 3, the inclination of the guide shaft 51 can be adjusted until an edge of the adjusting end 51b contacts the lower surface of the bracket 16. However, the guide shaft 51 may incline too much, and the optical pickup 30, guided by the guide shaft 51, may contact the lower surface of the disc D. Furthermore, when the bracket 16 coupled with the adjusting screw 61 is made of a thin metal plate as described above, a space between the adjusting end 51b and the bracket 16 is very large, so that the inclination of the guide shaft 51 has to be adjusted in a large portion. Further, in a case where the surface of the disc D is not perfectly planar, and is slightly warped, the above-described problems appear with increased frequency. As described above, when the optical pickup 30 contacts the lower surface of the disc D due to a large inclination of the guide shaft 51, the lower surface of the disc D is damaged, and the smooth rotation of the disc D is disturbed, resulting in an an error generated by the optical pickup 30 in recording and reproducing data.
Recently, as more compact optical disc players have been manufactured, the height thereof is small enough to allow use of optical disc players in portable computers, such as a notebook computer. Thus, since a space between a disc and a main base must be about 1 mm in a slim optical disc player for a portable computer, the above-described problems are frequently generated in the slim optical disc players.
When the inclination of the guide shaft 51 is adjusted as much as possible, the height H1 of the adjusting screw 61 protrudes above the bracket 16 is at a maximum value. A housing cover 90 is necessarily disposed at a position higher than the protruded height H1 of the adjusting screw 61, to prevent interference with the adjusting screw 61, thereby creating a large space between the housing cover 90 and the main base 10. Conventionally, to create a slim optical disc player and reduce the protruded height H1 of the adjusting screw 61, the diameter of the adjusting end 51b was made smaller than that of the guide shaft 51 shown in FIGS. 2 and 3. For example, if the diameter of the guide shaft 51 is 3 mm, the diameter of the adjusting end 51b is not bigger than 2 mm. Even though the protruded height H1 of the adjusting screw 61 is reduced, this results in an increase in the space between the adjusting end 51b and the bracket 16, and thereby, an increase in the frequency of appearance of the above-described problems.